1. Field of the Invention
The present invention relates to a method for manufacturing a semiconductor device, particularly, to a method for manufacturing a semiconductor device including a ferroelectric capacitor.
2. Description of the Related Art
A ferroelectric material such as lead zirconate titanate (PZT) or strontium bismuth tantalate (SBT) is used for forming a capacitor included in a ferroelectric memory. Such a ferroelectric material is weak against a reducing atmosphere such as a hydrogen atmosphere. If the ferroelectric material noted above is exposed to a hydrogen atmosphere, the oxygen atoms contained in the crystal of the ferroelectric material are extracted, with the result that the ferroelectric material fails to sufficiently exhibit a spontaneous polarization.
The conventional method for manufacturing a ferroelectric capacitor comprises, for example, the step of forming successively a lower electrode, a ferroelectric thin film and an upper electrode so as to form a laminate structure, followed by forming a hydrogen-resistant barrier film on the laminate structure. Then, a hard mask (HM) made of, for example, silicon dioxide is formed on the hydrogen-resistant barrier film, followed by processing the laminate structure in a desired pattern by a lithography process. In the lithography process, an organic anti-reflection layer is formed in general in order to prevent the reflection of the exposure light beam. Then, a photoresist film is formed so as to carry out the light exposure treatment. Each of the anti-reflection layer and the photoresist film can be formed by the coating of a material and the drying of the coated material, with the result that the manufacturing process can be simplified. After formation of a capacitor of a desired shape, the anti-reflection layer and photoresist film are removed by an oxygen plasma asher. What should be noted is that, during the treatment with the asher, a hydrogen gas is formed by the hydrogen atoms contained in the photoresist film and the anti-reflection layer. In other words, a hydrogen gas is generated during the treatment with the asher. The hydrogen gas thus generated is diffused through the HM (hard mask) to the ferroelectric capacitor. As a result, done to the capacitor is damaged.
After formation of the capacitor, metal wirings are formed with an interlayer insulating film interposed therebetween. A lithography process is also performed similarly in the step of forming the metal wirings. In the case of forming, particularly, a Cu wiring, a hydrogen annealing is performed in some cases as a pretreatment. It is possible for the hydrogen annealing to be a factor inducing damage to the capacitor.
In the case where a ferroelectric capacitor is formed on a transistor with an oxide film such as TEOS interposed therebetween, the capacitor is covered with a hydrogen barrier film such as Al2O3 in order to protect the capacitor from the hydrogen generated from the interlayer insulating film or in the step of forming the metal wiring. However, hydrogen permeates through the TEOS film formed in a lower portion or the TEOS film exposed to the outside in the step of forming the metal wiring and reaches the capacitor. As a result, the capacitor is damaged. It is possible to avoid the problem noted above if a hydrogen barrier is interposed between the TEOS film and the lower electrode. In this case, however, the number of manufacturing process steps and the manufacturing cost are increased.